I hope you all had a great day at TIAF today. This is my first time on this forum so sorry that my timing is a little off, and these information are probably irrelevant by the time you see them. But here it goes:
I have traveled to Japan many times by myself and I happened to catch TIAF in 2005 with my son during his spring break (during the same trip we also visited Aichi Expo, so it was a busy trip...). I guess you probably learned by now that you have to be at Big Sight incredibly early to line up if you wish to make it in the exhibit hall by the 10AM opening. However, even if you got stuck in the line, it would be a great experience among all the fans from all over Japan and all over the world.
Once I get in, I would try to go around all the booths very quickly first and snatch up free goodies, but really good stuffs may be gone already if you were stuck in the entry line, and many good stuffs require participation and that takes time, so it depends on what your priority is.
Food-wise I would suggest you bringing lunch with you, as I don't remember seeing many food vendors in Big Sight, and with this number of crowd, lining up to buy anything will be time consuming. Some onigiri are great lunch food to bring in your backpack or jacket pocket, especially if you haven't had this Japanese handy food before. I brought some Snickers with me from the U.S.; they always come in handy.
I generally would not suggest TIAF as one's first experience to Japan, since here at TIAF you are surrounded by one very specific type of Japaneses, and part of the idea behind cosplay is so that a Japanese doesn't have to be a Japanese himself. But if anime is the main or only thing you care about Japan, then TIAF and Akihabara are pretty much the two Holyland you have to cover.
That's my two bits. I imagine it would be an overwhelming experience for you as it was for me. I look forward to read about your feedback and discoveries from your TIAF visit.